Mobile wireless communications devices, such as cellular telephones and similar communications devices, include a housing and circuit board carried by the housing. A microprocessor, radio frequency (RF) transceiver and RF circuitry can be carried by the circuit board and operative with each other. An antenna could be located external or within the housing. A clock, such as a crystal oscillator, could be positioned external to the components and off the circuit board or mounted on the circuit board, and provide a clocking signal to the microprocessor, RF transceiver and other RF circuitry, including any Bluetooth modules, phase locked loop circuits, and local oscillator (LO) circuits. Typically, spurious signals and jitters caused by digital noise from a microprocessor creates problems because it shares the same clock with the RF circuits, such as the reference clock input to the phase locked loop. The clock from the crystal oscillator provides the reference clock input signal to both the RF circuits, such as the phased locked loop circuit, RF circuits and digital circuits, such as the microprocessor, but without buffering.
The microprocessor generates many digital noises that find their way back from the clock reference input of the microprocessor to the reference clock lines with which the RF circuits are sharing. These digital noises are conductively coupled to the RF circuits, including any RF transceiver, Bluetooth module and other RF circuits, such as a local oscillator and phase locked loop circuits, to cause spurious signals and jitters in the circuits, which in turn, degrade the RF performance or cause a radio to fail certain specifications.